Lapping is a well established process for finishing the tooth surfaces of bevel gears. It is a process that provides an economical alternative to other hard finishing processes for many applications of bevel gears. In testing, a pair of gears are rolled together and their rolling characteristics, such as radial and/or axial runout, meshing noise and contact pattern position, are determined and analyzed.
In the lapping process, a pinion and ring gear are mounted, via appropriate workholding equipment, to respective spindles in a lapping machine. In most instances of rolling of the gearset, the pinion is the driving member and the ring gear is braked. The gears are rolled in mesh and lapping compound or slurry, which can be a mixture of oil (or water) and silicon carbide or similar abrasive, is poured into the meshing zone. Testing machines generally have the same configuration as lapping machines although no abrasive material is utilized with a testing machine.
Most lapping and testing machines have three degrees of freedom available for realizing relative motion between a ring gear and pinion. The first freedom being relative movement in the direction of the ring gear axis which shall be referred to as direction G, the second freedom being relative movement in direction of the pinion axis which shall be referred to as direction H, and the third degree of freedom being distance between the ring gear and pinion axes which shall be referred to as direction V. The direction V is also known as the “hypoid offset.” While many lapping or testing machines have ring gear and pinion axes arranged with a fixed shaft angle of 90° with respect to one another, machines are also known in which the shaft angle between the ring gear and pinion is adjustable.
In lapping or testing processes, relative movement in the V and H directions effect positional changes in the contact pattern of the members of the gearset, in effect modifying the contact pattern. Lapping involves rotating the gear members in mesh with contact at a desired position on the tooth surfaces. Thus, the members are located at particular V and H positions along with a particular G direction position to effect the desired backlash.
Typically, the V, H and G movements each have an effect on both the lengthwise and depthwise position of the localized tooth contact pattern. As a gear set is lapped, contact is shifted toward one of the outer (heel) or inner (toe) portions of the tooth surface by changing the V and H settings as necessary to effect such a shifting of the contact position. As V and H are changed to effect the shifting, the G direction position must also be changed to maintain the desired backlash. When the desired heel or toe position is reached, V and H positions are again changed to shift contact to the other of the heel or toe positions with the changing V and H positions being accompanied by an appropriate G direction change to maintain backlash. The contact position is then returned to the beginning position.